The present invention relates generally to the field of latch mechanisms and, more particularly, to an extendable latch which secures an aircraft cowling to an engine pylon.
Modern jet engines are mounted to an aircraft with pylons or a similar support structure. A nacelle, in turn, is supported by both the engine and by the engine pylon. The nacelle is aerodynamically contoured to reduce aerodynamic drag during operation of the aircraft. The nacelle includes a pair of thrust reverser cowlings which form a large conical-shaped structure that wraps around the aircraft engine. These thrust reverser cowlings define an outer wall of the engine exhaust nozzle and must be capable of withstanding considerable hoop tension loads caused by the high pressure of the jet exhaust stream flowing therein.
The thrust reverser cowlings are normally connected by hinges to the engine pylon. The thrust reverser cowlings are hinged so that they can be pivoted upward to provide access to the engine for maintenance and repair. During aircraft operation, the thrust reverser cowlings must be pivoted downward, into closed positions, in which their ends are adjacent to one another or adjacent to an interposed strut.
The thrust reverser cowlings are attached at the top of each thrust reverser cowling, near the hinge line, to the engine pylon by remotely-actuated tension latches. Various types of tension latches mount and lock thrust reverser cowlings, to an engine pylon. A typical top-mounted latch includes a hook connected to the thrust reverser cowling used to engage a keeper mounted to the engine pylon. Further, the latch includes a remote handle which actuates the hook through a linkage. The latch incorporates an over-center position to establish rigid retention of the thrust reverser cowling to the engine pylon in the closed position.
A disadvantage of prior latches is that when the latches are closed, the linkages may or may not have been moved sufficiently such that it resumes the properly closed and over-center position. A further disadvantage of prior latches is that they need to be specifically designed for each model of aircraft. The latch for a particular aircraft model is designed to accommodate the distance between the thrust reverser cowling and the engine pylon required to allow the thrust reverser cowling to pivot between open and closed positions. For example, certain models of aircraft have the hinge points for the thrust reverser cowling close to where the latch will be attached to the engine pylon, thus, requiring the latch to accommodate a small distance. Conversely, other models of aircraft have the hinge points for the thrust reverser cowling distant from where the latch will be attached to the engine pylon requiring the latch to accommodate a long distance. Thus, each latch must be specifically designed for each model of aircraft. Unfortunately, this results in large amounts of resources being expended on research, design, and development to create particularized latches to be used with specific models of aircraft.
Prior latches have presented many problems when thrust reverser cowlings are closed. Top-mounted latches are not visible from the ground and must use remotely-actuated latch mechanisms which engage a keeper with a hook or opposing jaws. The hook or opposing jaws are connected to, and actuated by, a cable which in turn is connected to a handle located near the ground. This configuration allows a mechanic to open and close the latch from the ground at the bottom of the thrust reverser cowlings. When the latch is opened, the hook or opposing jaws disengage from the keeper allowing the thrust reverser cowling to be opened. After closing the thrust reverser cowling, the latch can be closed by use of the handle.
A disadvantage of these remotely-actuated latch mechanisms is that if the hook, opposing jaws, or keeper are not in the proper position, or are broken, it may still be possible to close the latch without engaging the keeper. Thus, resulting in a false indication that the latch is closed. A further disadvantage of the use of these remotely-actuated latch mechanisms is that there is no way for the mechanic to visually verify whether or not the hook or opposing jaws have properly engaged the keeper from the ground. Therefore, the mechanic operating the remotely-actuated latch mechanism can never be sure that the latch is properly closed.
Various devices, in conjunction with the previously described remotely-actuated latch mechanisms, have been used, unsuccessfully, to verify that the latch is properly closed. For example, previous attempts have been made to attach special devices such as sensors, feelers, or additional mechanisms to these latches to alert the mechanic when the hook or opposing jaws are not properly engaged to the keeper. The disadvantage of using these devices is that they are also subject to failure, damage, or human error.
In view of the above, it should be appreciated that there is a need for a latch that provides the advantages of having a linkage that; is secure in the closed and over-center position, ensures the linkage resumes the closed and over-center position when the latch is properly closed, designed to accommodate different distance requirements for the thrust reverser cowling to pivot between open and closed positions, and most importantly, is permanently connected to a keeper on the engine pylon. Therefore, eliminating the need for special devices used to verify that the latch is properly closed. The present invention satisfies these and other needs and provides further related advantages.
The present invention resides in an extendable latch. The extendable latch provides advantages over known latches in that it provides a linkage which is secure in the closed and over-center position, ensures that the linkage resumes the closed and over-center position when the extendable latch is properly closed, is designed to accommodate different distance requirements for the thrust reverser cowling to pivot between open and closed positions, and is permanently connected to a keeper on the engine pylon. Thus eliminating the need for special devices used to verify that the latch is properly closed. Furthermore, the extendable latch, in combination with other features described below, possesses a unique relationship of slots, links, and a spring that enables the latch to open and close without the problems inherent in the disengagement and re-engagement of the latch from the keeper.
The extendable latch is used for securing a thrust reverser cowling to an engine pylon. The extendable latch is connected to one end of a push/pull cable. The other end of the push/pull cable is connected to a handle which also has an open and a closed position. Preferred embodiments of the extendable latch include a housing, an extendable linkage, a keeper bar, a strut, and a detent mechanism. The housing includes a first wall and a second wall that are aligned with and positioned parallel to each other. The extendable linkage is rotatably mounted to the housing. The strut has a central axis and opposing ends with one end of the strut rotatably mounted to the extendable linkage, and the other end of the strut rotatably mounted to the keeper bar. Also, the detent mechanism is rotatably mounted to both the housing and the extendable linkage. The detent mechanism has a blocking position in which the detent mechanism is adjacent the strut. The detent mechanism also has an unblocking position in which the detent mechanism is away from the strut.
In another alternative embodiment of the invention, at least one step rivet, having a center region, rotatably mounts the extendable linkage to the housing. Also, the end of the strut that mounts to the extendable linkage includes a collar. A pin inserts through the collar rotatably mounting the strut to the extendable linkage. Also, a mounting keeper rotatably mounts the strut to the keeper bar. In addition, this embodiment has an over-center position where the collar is located between the first and second walls and the central axis of the strut is located below the center region of the step rivet. The over-center position is such that it prevents the strut from inadvertently moving.
In this embodiment of the invention, the detent mechanism includes a blocking link and a connecting link, both with opposing ends. One end of the blocking link is rotatably mounted to the housing. The other end of the blocking link is adjacent the strut when the detent mechanism is in the blocking position. Also, one end of the connecting link is rotatably mounted to the extendable linkage. The other end of the connecting link is rotatably mounted to the blocking link.
An additional embodiment of the invention includes an extendable linkage having a plurality of adjacent links which telescope in and out of one another. Additionally, each of the plurality of adjacent links has at least one stepped protrusion. The stepped protrusion of each link mates with the stepped protrusion of another adjacent link such that each link is connected to an adjacent link.
In yet another embodiment of the invention, the extendable linkage includes a base link and a plurality of other links. The base link and the plurality of other links telescope in and out of one another. The step rivet mounts through a base link slot in each base link. Also, the base link and each of the plurality of other links has at least one stepped protrusion. Each stepped protrusion of each link mates with the stepped protrusion of each adjacent link such that each link is connected to its respective adjacent link.
An advantage of the present invention is that the detent mechanism overcomes the difficulties associated with prior latches which are prone to be moved from their respective closed and over-center positions due to forces encountered during flight. The action of the detent mechanism secures the strut such that the present invention is less likely to open. Therefore, the extendable latch is inherently stable and is not prone to inadvertently open.
A related advantage of the detent mechanism is that it ensures that the strut resumes the over-center position when the extendable latch is closed. As the extendable latch is closed, the blocking link of the detent mechanism engages the strut and pushes the strut back into the over-center position. Therefore, when an operator closes the extendable latch, the operator can be assured that the strut has resumed the over-center position and that the thrust reverser cowling is rigidly latched to the engine pylon.
A feature of the present invention is that it includes an extendable linkage with a plurality of links which telescope in and out of each other, thus, accommodating different distance requirements. Also, by simply adjusting the number and/or the length of the plurality of links used in the extendable linkage, the extendable latch can be used with even a greater variety of aircraft whose distance requirements may not initially fit within the reach of the extendable latch.
An additional advantage of the present invention is the unique relationship of slots, links, and a spring that allow the strut and the mounting keeper to remain securely engaged, i.e., permanently connected, thus, ensuring that; the mounting keeper is always properly engaged to the strut, the latch will always close properly, and a potentially unsafe condition will not occur. This is important because the extendable latch is mounted at the top of the thrust reverser cowling, near the hinge line, where an operator of the extendable latch cannot visually verify whether or not the extendable latch has properly closed.
A further advantage of the present invention is that no special devices need be used to alert an operator that the extendable latch is not properly engaged to the mounting keeper since the extendable latch is permanently connected to the mounting keeper. This is advantageous because these special devices, such as sensors and feelers, are subject to failure, damage, or human error in using them. A further related advantage of the elimination of these special devices is the corresponding elimination of extra cost and weight.
An additional feature of the present invention is that the slots, links, and spring prevent the extendable latch from becoming bound during opening and closing of the thrust reverser cowlings. This is advantageous because the thrust reverser cowlings must be opened and closed in a short period of time to perform required engine repair and/or maintenance. If problems were to occur in the opening and closing of the thrust reverser cowlings due to the latch mechanism, extra time would have to be spent to repair the latch mechanism instead of the aircraft, resulting in extra cost and delayed flight times for the aircraft.
Other features and advantages of the present invention will be set forth in part in the description which follows and the accompanying drawings, wherein the preferred embodiments of the present invention are described and shown, and in part will become apparent to those skilled in the art upon examination of the following detailed description taken in conjunction with the accompanying drawings, or may be learned by practice of the present invention. The advantages of the present invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.